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Medically reviewed by
Dr Daniel Atkinson
Clinical Reviewer
on September 29, 2022.
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Chantix pills side effects

Some people find the prospect of side effects discouraging without realizing that the withdrawal from nicotine-based products can come with its own range of side effects. Many people who quit smoking experience weight gain, increased irritability, nausea, and flu-like symptoms. Taking smoking cessation drugs such as Chantix can help lessen these side effects and make the process of giving up nicotine more achievable and successful in the long run.

All medications and treatments available over the counter or by prescription come with the potential for side effects. For this reason, it’s incredibly important to read the patient information leaflet provided with your medications in order to familiarize yourself with said side effects.

When used successfully, Chantix can help you lead a smoke-free life, but those thinking about taking it should be aware of any varenicline side effects, ranging from the more minor ones to the more serious ones. If you are concerned about any of the listed side effects of Chantix, don’t hesitate to reach out to your prescriber.

What are the most common side effects of Chantix

  • Very common
  • Uncommon
  • Rare
  • Unknown

The most common side effects (affecting up to one in 10 people taking Chantix) include;

  • Inflammation of the nasal passages
  • Abnormal dreams
  • Headaches
  • Nausea
  • Insomnia.

Less common side effects (affecting up to one in 100 people) include; 

  • Weight gain
  • Fluctuation in appetite
  • Drowsiness
  • Sinus inflammation
  • Chest infections
  • Shortness of breath
  • Dizziness
  • Heartburn
  • Coughing
  • Constipation
  • Diarrhea
  • Bloating
  • Toothache
  • Abdominal pain
  • Irritation of the skin
  • Aching joints or muscles
  • Back pain

Rare side effects of taking Chantix include 

  • Flu-like symptoms
  • Mood swings
  • Depression
  • Restlessness
  • Tremors
  • Viral or fungal infections
  • Mouth ulcers
  • Conjunctivitis
  • Tinnitus (ringing in the ears)
  • Strokes
  • Irregular heartbeat
  • Loss of coordination 
  • Loss of sex drive
  • Increased muscle tension
  • Difficulty speaking
  • Vaginal discharge
  • Hallucinations
  • Sight problems
  • Hot flushes
  • Upset stomach
  • High blood pressure
  • Increased heart rate
  • Bloody stools
  • Increased perspiration
  • A fever.

These affect up to one in a 1000 users of Chantix.

Whilst it is still unknown what the effects might be, it’s not advised to take Chantix during pregnancy or nursing an infant due to the potential for the drug to be transferred to the fetus or the child.

Chantix : serious side effects

It’s important to be aware of the more serious side effects of Chantix before you decide to begin treatment. If you’re concerned about them, consult your GP or prescribing clinician to discuss these concerns further.

Many of the serious side effects of Chantix occur infrequently. Seeking the help or advice of a medical professional will help reassure you on what is best for you and will help you weigh up the benefits over the risks.

While some prescribers may not actively advise against drinking alcohol whilst taking Chantix, there is still a chance that the two substances can negatively interact. 

Some people who have mixed alcohol and Chantix have reported that their tolerance for alcohol is much lower, and they become intoxicated at a much more elevated rate. Additionally, they report that their potential for alcohol-induced blackouts increases, and they can become aggressive or rowdy more easily. At the very least, it’s wise to limit alcohol intake whilst using Chantix. 


That said, some studies have suggested that varenicline can help reduce alcohol intake in alcohol-dependent individuals, quelling an individual’s cravings for alcohol in a similar way to how it staves off nicotine cravings . However, there is insufficient evidence to support this hypothesis.

One of the potential side effects of Chantix that causes people some concern is weight gain. However, it’s worth noting that quitting smoking can cause weight gain on its own. This is because smoking suppresses appetite and speeds up metabolism.
Additionally, whilst weight gain is listed as a potential side effect of Chantix, very few people do actually put on weight whilst taking the treatment. In fact, some studies regarding Chantix weight gain have shown that users do not gain more weight on Chantix than without .

In some cases, Chantix can cause adverse gastrointestinal effects, such as constipation, but this is quite an uncommon side effect. Quitting smoking can also cause constipation, it’s not always easy to work out the underlying cause. One study showed that one in 24 subjects treated with varenicline (the main ingredient found in Chantix) experienced constipation .

A concern amongst many individuals thinking about taking Chantix is the prospect of a loss of libido.

However, a decreased libido is an uncommon side effect experienced by roughly one in 1000 users of Chantix. Additionally, in those rare cases that Chantix does affect sex drive, it can also lead to an increased libido.

It has been reported that Chantix can cause issues with sleep. However, it’s important to remember that restlessness and difficulty sleeping can also be generic symptoms of nicotine withdrawal.

Some studies have found that abnormal dreams and sleeping patterns are common side effects of taking varenicline, but these symptoms often subside after the first few weeks after beginning treatment . Taking your evening dosage immediately after your evening meal and not straight before bedtime can help reduce the sleep-related side effects of Chantix.

That said, it’s essential to talk to one of our doctors or consult your family practitioner if you feel these symptoms becoming more extreme or if you begin to experience sleep aggression or sleepwalking.

How long do Chantix side effects last?

A usual course of Chantix treatment lasts for around 12 weeks. Within these initial few weeks, you may begin to experience some side effects, such as some of those listed above. You shouldn’t become disheartened if you experience minor side effects when taking Chantix. It is still one of the safest smoking cessation treatments available and is a lot safer than smoking cigarettes.

To date, there have been no sufficient studies to suggest any Chantix side effects are long term. That said, there have been a small number of reports from patients who’ve taken Chantix that claim there was an impact on their mood even after stopping the treatment.

If your side effects persist or become more severe, consult your prescribing clinician for advice on your next best steps.

What happens when you stop taking Chantix

promise1-1.svgPeople who suddenly discontinue their Chantix treatment may experience some side effects or withdrawal symptoms. Chantix withdrawal side effects may include feelings of depression, irritability, difficulty sleeping, and the urge to smoke again, leading to a potential relapse.

For this reason, if you wish to stop your Chantix treatment, your doctor may advise that you gradually reduce your dosage over a week or two.

What to do if you experience Chantix side effects

If you experience any side effects whilst taking Chantix, you should inform your prescribing doctor immediately. As discussed, the side effects of suddenly stopping Chantix can cause relapses, so it’s best to discuss your options with a clinician before stopping treatment.

If you are prescribed Chantix but find that it does not work for you for whatever reason, your prescribing doctor will be able to find alternative stop smoking treatments for you. There are plenty of other medical aids available which can help you kick smoking successfully.

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This page was medically reviewed by Dr Daniel Atkinson, Clinical Reviewer on September 29, 2022. Next review due on September 29, 2024.

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